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m42 to FX..or other.. macro focusing helicoid adapter
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PostPosted: Fri Dec 20, 2019 9:24 pm    Post subject: m42 to FX..or other.. macro focusing helicoid adapter Reply with quote

I am wondering how useful this adapter is.
On ebay some focus to infinity and some do not. Can be used for macro.
Does any one have any experience on their mirrorless camera?

Thank you.


PostPosted: Fri Dec 20, 2019 10:09 pm    Post subject: Reply with quote

I'm using several of these macro helicoid adapters like Minolta MD or Leica-M to Sony E. They are quite useful to shorten the MFD whilst still maintaining infinity.
However, the possible macro magnification greatly depends on the used lens.
There are also some special helicoid adapters for the use of enlarger lenses. In this case the register distance for infinity of the lens in question is quite important to find the right adapter.


PostPosted: Fri Dec 20, 2019 11:15 pm    Post subject: Reply with quote

I agree with everything tb_a said.
There are some caveats: cheap helicals can have some play when partially extended. Doesn't influence IQ, just mechanical satisfaction.
Lenses with large image circle can have poor contrast and/or hotstpot problems when extended a lot.

I use these things for bokeh-shooting.

Extension tubes, I hear someone say? Forgot what that is, sorry.


PostPosted: Sat Dec 21, 2019 8:59 am    Post subject: Reply with quote

tb_a wrote:
I'm using several of these macro helicoid adapters like Minolta MD or Leica-M to Sony E. They are quite useful to shorten the MFD whilst still maintaining infinity.
However, the possible macro magnification greatly depends on the used lens.
There are also some special helicoid adapters for the use of enlarger lenses. In this case the register distance for infinity of the lens in question is quite important to find the right adapter.


Thanks for the information.
Can you give some examples to illustrate "However, the possible macro magnification greatly depends on the used lens." I
am curious what kind of magnification can be had.

aidaho wrote:
I agree with everything tb_a said.
There are some caveats: cheap helicals can have some play when partially extended. Doesn't influence IQ, just mechanical satisfaction.
Lenses with large image circle can have poor contrast and/or hotstpot problems when extended a lot.


Thanks.
Could I use them with a 200mm lens? It would be to get closer focus, not necessarily for macro.


PostPosted: Sat Dec 21, 2019 9:09 am    Post subject: Reply with quote

uddhava wrote:

Thanks.
Could I use them with a 200mm lens? It would be to get closer focus, not necessarily for macro.

You can use them with 200mm, but like tb_a said, with longer lenses extensions of any kind hit diminishing returns.
So yes, you will be able to focus closer, just not nearly as close as with shorter focal lenghts.

I did a quick measurement and my EF helical extends 15mm.
You can try a 15mm extension ring and get an idea on how useful the adapter would be for your needs.


PostPosted: Sat Dec 21, 2019 2:21 pm    Post subject: Reply with quote

[quote="aidaho"]
uddhava wrote:


I did a quick measurement and my EF helical extends 15mm.
You can try a 15mm extension ring and get an idea on how useful the adapter would be for your needs.


I think most of my helicoids extend more than that, the range I've seen available go from 12-17mm (5mm max extension) up to 36-90mm (54mm extension).

Those that give infinity focus are ideal for short to normal focal lengths, working as a normal adapter most of the time but just adding an adjustable extension tube when closer focus is wanted.
The longer ones (often mounted via a short M42 adapter rather than being sold in the cameras lens mount) are ideal for adapting the likes of enlarger/projector lenses which have no focusing mechanism of their own.

You can get an idea of how close you'll be able to focus by playing with the thin lens formula 1/focal length=1/subject distance + 1/image distance.
Apply it once to find the image distance at the lenses MFD, then add extension to that & reapply it to find the new MFD, or just use image distance = focal length+extension to see the focusing distance with the extended lens at infinity.

Taking a 50mm lens with a MFD of 300mm as an example that 15mm extension would make the lenses new focusing range roughly 215-150mm - in this case the 15mm helicoid halves the MFD when extended, yet should still allow infinity focus when at it's shortest. They become even more useful with fisheye lenses where you can't get short enough tubes to use tham extended Smile


PostPosted: Sun Dec 22, 2019 9:16 am    Post subject: Reply with quote

Thank you for all the information!
Now I will buy one and see how it works.